#include <bits/stdc++.h>
using namespace std;
int main() {
	double a,b,c;
	cin >> a >> b >> c;
	double p = (a + b + c) / 2;
	
	double ret=sqrt(p * (p - a) * (p - b) * (p-c));
	printf("%.1lf", ret);
	return 0;
}
